Melioidosis

Melioidosis is an infectious disease caused by a Gram-negative bacterium called Burkholderia pseudomallei. Signs and symptoms can range from none to mild such as fever, skin changes, pneumonia, and abscesses to severe with inflammation of the brain, inflammation of the joints with dangerously low blood pressure which could easily results in death. Melioidosis is an infectious disease caused by a Gram-negative bacterium called Burkholderia pseudomallei. Signs and symptoms can range from none to mild such as fever, skin changes, pneumonia, and abscesses to severe with inflammation of the brain, inflammation of the joints with dangerously low blood pressure which could easily results in death. The bacteria can be transmitted through wounds, inhalation, and ingestion of polluted water. Person-to-person or animal-to-human transmission is extremely rare. The infection is constantly present in Southeast Asia particularly in northeast Thailand and in northern Australia. In developed countries such as Europe and United States, melioidosis cases are usually imported from countries where melioidosis are constantly present. Diagnosis is usually confirmed by the growth of the bacteria in growth medium. It is important to differentiate the disease clinically from tuberculosis because both shared similar signs and symptoms with similar chest radiograph findings. If the disease is properly treated, death rate is 10%, but if the disease if improperly treated, the death rate could be more than 40%. Efforts to prevent the disease includes: wearing protective gear while handling contaminated water or apparatus, avoiding direct contact with soil, water, or heavy rain, practising hand hygiene, and drinking boiled water. Antibiotic co-trimoxazole is only used for high risk individuals for getting the disease after being exposed to the bacteria. There is no approved vaccines for melioidosis yet. Treatment if infected is with ceftazidime, meropenem, and co-trimoxazole. It is estimated that 165,000 people are infected by melioidosis per year. This results in about 89,000 deaths per year. Increased rainfall is associated with increased number of melioidosis cases in endemic areas. The disease was first described by Alfred Whitmore in 1912 in present-day Myanmar. Most of the people who are exposed to the bacteria experience no symptoms. For those children staying in endemic areas, 25% of them experienced seroconversion (the time period needed for antibodies started to form against antigens) in between 6 months to 4 years. This means that high number of asymptomatic people will be tested positive in serology in endemic areas. In Thailand, the seropositivity rate exceeds 50% while for Australia, the seropositivity is only 5%. The mean incubation period of acute melioidosis was 9 days (range 1–21 days). Symptoms usually appear 2 to 4 weeks after exposure. However, symptoms of melioidosis can also appear in 24 hours for those experienced near drowning in water. Those affected are presented with symptoms of sepsis (predominantly fever) with or without pneumonia, or localised abscess or other focus of infection. The presence of non-specific signs and symptoms has caused melioidosis to be nicknamed as 'the great mimicker'. 85% of the melioidosis cases are acute. Those people with diabetes mellitus or occupation or seasonal exposure to the bacteria are at increased risk of developing melioidosis. The disease should be considered in anyone who has fever and staying in endemic areas and those who has abscesses in liver, spleen, prostate, or parotid gland with pneumonia. The clinical manifestation of the disease can range from simple skin changes to severe organ involvement. In northern Australia, 60% of the infected children presented with skin lesions only while 20% of them presented with pneumonia. Among the commonest organs affected are: liver, spleen, lungs, prostate, and kidneys. Bacteremia can occur in 40 to 60% of the people while septic shock occurs in 20% of the cases. Pneumonia is present in 50% of the cases. For those presented with septic shock together with pneumonia, there could be minimal cough. However, for those presented with pneumonia only, prominent cough with sputum and shortness of breath is observed. On chest X-ray, the appearance could range from diffuse nodular infiltrates in those with septic shock to progressive pulmonary consolidation in the upper lobes for those presented with pneumonia only. Pleural effusion and empyema are more common for melioidosis affecting lower lobes of the lungs. Therefore, melioidosis should be differentiated from tuberculosis for those coming from endemic areas because both conditions show radiogical changes on the upper lobes of the lungs. In 10% of the cases, there are secondary pneumonia caused by other bacteria after the primary infection. 1% to 5% of those infected could develop encephalomyelitis or brain abscess, 14 to 28% of the cases could develop acute pyelonephritis, kidney abscess or prostatic abscesses, 0 to 30% would develop neck or parotid gland abscess, 10 to 33% would develop liver, spleen, or paraintestinal abscesses and 4 to 14% of the cases could develop septic arthritis and osteomyelitis. Other rare manifestations could be lymphadenopathy resembling tuberculosis, mediastinal masses, pericardial effusion, mycotic aneurysm, and pancreatitis. Specifically in Australia, up to 20% of the males can get prostatic abscess. Presentation for prostatic abscesses are: pain during urination (dysuria), difficulty in passing urine, and urinary retention requiring catheterization. Rectal examination shows tender and boggy prostate. In Thailand, 30% of the infected children can get parotid abscess. Subconjunctival abscess and orbital cellulitis may also occur. Encephalomyelitis can occur in healthy people without risk factors. Computed tomography (CT) brain is normal but there is an increase in T2 signal on magnetic resonance imaging (MRI), extending to brain stem and spinal cord. Clinical signs include: unilateral upper motor neuron limb weakness, cerebellar signs, and cranial nerve palsies (VI, VII nerve palsies and bulbar palsy). Some cases presented with flaccid paralysis alone. In northern Australia, all melioidosis with encephalomyelitis cases have elevated white cells in cerebrospinal fluid (CSF), measuring at 30 to 775 cells per microlitres, where majority of the cells are mononuclear cells. CSF protein can be elevated with normal glucose levels. Chronic melioidosis is usually defined by a duration of symptoms greater than two months and occurs in about 10% of patients. The clinical presentation of chronic melioidosis is protean and includes such presentations as chronic skin infections, chronic lung nodule, and pneumonia. In particular, chronic melioidosis closely mimics tuberculosis, and has sometimes been called 'Vietnamese tuberculosis'. Other clinical presentations include: fever, weight loss, productive cough with or without bloody sputum with long standing abscesses at multiple body sites.